1. Field of the Invention
The present invention relates generally to optical head devices for use in disc players, and more particularly, to an optical head device which causes a light beam to impinge upon an optical record disc and guides the light beam from the optical record disc to a photodetector for reproducing information recorded on the optical record disc and is further operative to maintain the light beam incident upon the optical record disc in correct tracking and focus relations to a record track formed on the optical record disc.
2. Description of the Prior Art
In an optical disc player for reproducing information recorded on an optical record disc, an optical head device is provided for constituting an optical arrangement to read information from a record track formed on the optical record disc by the use of a laser light beam impinging upon the record track. The optical head device is required to produce the laser light beam, cause the laser light beam to impinge upon the record track, which is usually very narrow in width, so as to trace the same, and guide properly a reflected laser light beam obtained from the optical record disc to a photodetector. Further, the optical head device is also required to maintain the laser light beam incident upon the optical record disc in correct focus and tracking relations to the record track on the optical record disc.
For fulfilling these requirements, the optical head device comprises a precise arrangement of various optical components including a semiconductor laser for generating a laser light beam, an objective lens disposed for facing the optical record disc, other lenses, mirrors, prisms, photodetecting elements and so on, which is supported to be movable in both directions along an optical axis of the objective lens and perpendicular to the optical axis of the objective lens. This results in a disadvantage that the optical head device is apt to need troublesome adjusting work for each optical component and a relatively large space in which the various optical components are disposed and moved in the directions along the optical axis of the objective lens and perpendicular to the optical axis of the objective lens.
In view of this, as disclosed in the Japanese patent application published before examination under publication number 62-283430, there has been proposed an optical head device having an integrated light generating and receiving unit which comprises a semiconductor substrate on which a photodetector, a semiconductor laser, and a prism for directing a laser light beam generated by the semiconductor laser to the outside of the unit to be caused to impinge upon the optical record disc and for guiding a reflected laser light beam obtained from the optical record disc to the photodetector, as an optical head device intended to avoid the above mentioned disadvantage.
In such an optical head device provided with the integrated light beam generating and detecting unit as described above, the integrated light beam generating and detecting unit, a single mirror and an objective lens are supported by a common support member. The laser light beam which is generated by the semiconductor laser and directed by the prism to the outside of the unit is reflected by the mirror disposed on an optical axis of the objective lens to enter the objective lens and caused to impinge upon the optical record disc through the objective lens. Then, the reflected laser light beam from the optical record disc returns through the objective lens and is reflected by the mirror to enter the prism of the integrated light beam generating and detecting unit. In the integrated light beam generating and detecting unit, the reflected laser light beam is guided by the prism to the photodetector.
The support member supporting the integrated light beam generating and detecting unit, the single mirror and the objective lens in common is mounted on a driving mechanism and moved by the driving mechanism in both the direction along the optical axis of the objective lens and the direction perpendicular to the optical axis of the objective lens, so that the laser light beam incident to the optical record disc through the objective lens is subjected to a focus servo control by which the laser light beam incident upon the optical record disc is controlled to be maintained in correct focus relation to a record track formed on the optical record disc and subjected also to a tracking servo control by which the laser light beam incident upon the optical record disc is shifted in the direction perpendicular to the optical axis of the objective lens to be maintained in correct tracking relation to the record track formed on the optical record disc.
As described above, in the previously proposed optical head device having the integrated light beam generating and detecting unit, since an optical system for causing the laser light beam to impinge upon the optical record disc and receiving the reflected laser light beam from the optical record disc is constituted with the integrated light beam generating and detecting unit, the single mirror and the objective lens each supported in common by the support member, portions requiring troublesome adjustments are reduced and the device occupies a relatively small space.
However, in the optical head device having the integrated light beam generating and detecting unit, since an optical path formed between the integrated light beam generating and detecting unit and the objective lens is changed in direction once at the mirror, the integrated light beam generating and detecting unit has to be disposed to have its longitudinal direction along the optical axis of the objective lens and further, in the case where the optical path from the integrated light beam generating and detecting unit to the objective lens is made relatively long so that the numerical aperture of the objective lens is selected to be sufficiently large, the space between the mirror and the objective lens becomes relatively large. Consequently, the size of the device in the direction along the optical axis of the objective lens, that is, the thickness of the device, is not reduced enough so that the device can not be miniaturized in overall thickness. Further, although the optical path for the laser light beam can be adjusted be means of adjusting only the mirror, the degree of freedom in adjustment of the mirror is too large and therefore it is difficult to adjust precisely the optical path for the laser light beam.